Apparatus and method for purging injection molding system

ABSTRACT

An injection molding apparatus, system and method are provided in which the rate of material flow during the injection cycle is controlled. According to one preferred embodiment, a method of open-mold purging is provided in an injection molding system including a manifold to receive material injected from an injection molding machine. The method includes the steps of selecting a target purge pressure; injecting material from the injection molding machine into the manifold; and controlling the purge pressure to substantially track the target purge pressure, wherein the purge pressure is controllable independently from the injection molding machine pressure.

RELATED APPLICATIONS

This application is a Continuation-in-Part under 35 U.S.C. §120 of U.S.application Ser. No. 09/503,832, filed Feb. 15, 2000 which is aContinuation-in-Part of U.S. application Ser. No. 09/400,533. entitled“MANIFOLD SYSTEM HAVING FLOW CONTROL”, filed Sep. 21, 1999, which is aContinuation-in-Part of U.S. application Ser. No 09/063,762, entitled“MANIFOLD SYSTEM HAVING FLOW CONTROL” filed Apr. 21, 1998, and claimspriority under 35 U.S.C. §119(e) to Provisional Application Ser. No.60/156,925, entitled “DYNAMIC FEED CONTROL” filed Sep. 28, 1999, andProvisional Application Ser. No. 60/152,714, entitled “DYNISCO DYNAMICFEED CONTROL SYSTEM OPEN-MOLD PURGE” filed Sep. 7, 2000.

FIELD OF THE INVENTION

This invention relates to injection of pressurized materials through amanifold, such as injection molding of plastic melt in a hot runnersystem. More specifically, this invention relates to an improvedinjection molding hot runner system in which the rate of melt flow iscontrolled through the gate during an injection molding cycle.

DESCRIPTION OF THE RELATED ART

U.S. Pat. No. 5,556,582 discloses a multi-gate single cavity system inwhich the rate of melt flow through the individual gates is controlledindependently via a control system according to specific target processconditions. This system enables the weld line of the part (the sectionof the part in which the melt from one gate meets the melt from anothergate) to be selectively located. It also enables the shape of the weldline to be altered to form a stronger bond.

The '582 patent discloses controlling the rate of melt flow with atapered valve pin at the gate to the mold cavity. It also disclosesplacing a pressure transducer inside the mold cavity. Placing thepressure transducer inside the mold cavity can result in the pressuretransducer sensing pressure spikes which can occur when the valve pin isclosed. A pressure spike sensed by the transducer can cause anunintended response from the control system, and result in a lessprecise control of the melt flow than desired.

The control system disclosed in the '582 patent uses the variables ofvalve pin position and cavity pressure to determine what position thevalve pin should be in. Thus, the algorithm performed by the controlsystem in the '582 patent utilizes two variables to control the rate ofmelt flow into the cavity.

SUMMARY OF THE INVENTION

An injection molding apparatus, system and method are provided in whichthe rate of material flow during the injection cycle is controlled.According to one preferred embodiment, a method of open-mold purging isprovided in an injection molding system including a manifold to receivematerial injected from an injection molding machine. The method includesthe steps of selecting a target purge pressure; injecting material fromthe injection molding machine into the manifold; and controlling thepurge pressure to substantially track the target purge pressure, whereinthe purge pressure is controllable independently from the injectionmolding machine pressure.

According to another illustrative embodiment, an injection moldingsystem is provided that includes a mold, an injection molding machine, amanifold, and a controller used to control open mold purging of themanifold. The controller controls a pressure of material used to purgethe manifold, independently from the injection molding machine injectionpressure.

According to another illustrative embodiment, an injection moldingsystem is provided that includes a manifold to deliver material into amold that is injected into the manifold from an injection moldingmachine; and a controller used to control open mold purging of themanifold, the controller to control a pressure of material used to purgethe manifold, independently from the injection molding machine injectionpressure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partially schematic cross-sectional view of an injectionmolding system according to one embodiment of the present invention;

FIG. 2 is an enlarged fragmentary cross-sectional view of one side ofthe injection molding system of FIG. 1;

FIG. 3 is an enlarged fragmentary cross-sectional view of an alternativeembodiment of a system similar to FIG. 1, in which a plug is used foreasy removal of the valve pin;

FIG. 4 is an enlarged fragmentary cross-sectional view of an alternativeembodiment of a system similar to FIG. 1, in which a threaded nozzle isused;

FIG. 5 is a view similar to FIG. 4, showing an alternative embodiment inwhich a plug is used for easy removal of the valve pin;

FIG. 6 shows a fragmentary cross-sectional view of a system similar toFIG. 1, showing an alternative embodiment in which a forward shut-off isused;

FIG. 7 shows an enlarged fragmentary view of the embodiment of FIG. 6,showing the valve pin in the open and closed positions, respectively;

FIG. 8 is a cross-sectional view of an alternative embodiment of thepresent invention similar to FIG. 6, in which a threaded nozzle is usedwith a plug for easy removal of the valve pin;

FIG. 9 is an enlarged fragmentary view of the embodiment of FIG. 8, inwhich the valve pin is shown in the open and closed positions;

FIG. 10 is an enlarged view of an alternative embodiment of the valvepin, shown in the closed position;

FIG. 11 is a fragmentary cross sectional view of an alternativeembodiment of an injection molding system having flow control thatincludes a valve pin that extends to the gate;

FIG. 12 is an enlarged fragmentary cross-sectional detail of the flowcontrol area;

FIG. 13 is a fragmentary cross sectional view of another alternativeembodiment of an injection molding system having flow control thatincludes a valve pin that extends to the gate, showing the valve pin inthe starting position prior to the beginning of an injection cycle;

FIG. 14 is view of the injection molding system of FIG. 13, showing thevalve pin in an intermediate position in which material flow ispermitted;

FIG. 15 is a view of the injection molding system of FIG. 13, showingthe valve pin in the closed position at the end of an injection cycle;and

FIG. 16 shows a series of graphs representing the actual pressure versusthe target pressure measured in four injection nozzles coupled to amanifold as shown in FIG. 13;

FIGS. 17 and 18 are screen icons displayed on interface 114 of FIG. 13which are used to display, create, edit, and store target profiles;

FIG. 19 is a fragmentary cross-sectional partially schematic view ofanother alternative embodiment of an injection molding system havingflow control in which a ram is used to inject material from a well inthe manifold into the mold cavity;

FIG. 20 is a fragmentary view of the embodiment shown in FIG. 19 inwhich the well 640 is being filled by the injecting molding machine;

FIG. 21 is a view similar to FIG. 20 in which the well is full ofmaterial and the system is ready to inject material into the moldcavity;

FIG. 22 is a view similar to FIGS. 20 and 21 in which injection into themold cavity has begun;

FIG. 23 is a view similar to FIGS. 20-22 in which the injection cycle iscomplete;

FIG. 24 is a cross-sectional partially schematic view of anotheralternative embodiment of an injection molding system having flowcontrol in which a load cell behind the valve pin is used to control theflow rate in each injection nozzle;

FIG. 25 is a enlarged fragmentary cross-sectional view of the valve pinand actuator of FIG. 24;

FIG. 26 is an enlarged view of the load cell and valve pin of FIG. 24;

FIGS. 27A and 27B show an enlarged view of the tip of the valve pinclosing the gate and controlling the flow rate, respectively;

FIGS. 28A and 28B shown an alternative structure of an injection moldingnozzle for use in the system shown in FIG. 24;

FIG. 29 is a cross-sectional partially schematic view of an alternativeembodiment of an injection molding system having flow control similar toFIG. 19 in which a pressure transducer is used to sense the hydraulicpressure supplied to the actuator;

FIG. 30 shows a fragmentary cross-sectional view of an alternativeembodiment of an injection molding system having flow control similar toFIG. 13 in which the pressure transducer is mounted in the mold cavity;and

FIG. 31 is a fragmentary cross-sectional view of an alternativeembodiment of an injection molding system having flow control in whichflow control is achieved by measuring the differential pressure of theactuator chambers.

FIG. 32 is a schematic representation of an injection molding systemutilizing the hot runner system shown in FIG. 1;

FIG. 33 is an alternative embodiment of the system of FIG. 32 in whichthe hydraulic power source associated with the servo valves 802 has beenintegrated with the injection molding machine hydraulic power unit;

FIG. 34 is an alternative embodiment of the injection molding systemsshown in FIGS. 32 and 33 in which the controller 804 and operatorinterface 805 have been integrated in the injection molding machinecontroller 830 and interface 832;

FIG. 35 is an alternative embodiment of the injection molding system ofFIG. 32 in which the cavity pressure transducers 824 and 826 are locatedat the end of two mold cavities 5 a and 5 b;

FIG. 36 is a flow chart depicting an illustrative embodiment of a methodof open mold purging; and

FIG. 37 is a representation of a screen icon generated on interface 214,showing actual and target purge pressure profile traces.

DETAILED DESCRIPTION

FIGS. 1-2 show one embodiment of the injection molding system accordingto the present invention. The injection molding system 1 is a multi-gatesingle cavity system in which melt material 3 is injected into a cavity5 from gates 7 and 9. Melt material 3 is injected from an injectionmolding machine 11 through an extended inlet 13 and into a manifold 15.Manifold 15 distributes the melt through channels 17 and 19. Although ahot runner system is shown in which plastic melt is injected, theinvention is applicable to other types of injection systems in which itis useful to control the rate at which a material (e.g., metallic orcomposite materials) is delivered to a cavity.

Melt is distributed by the manifold through channels 17 and 19 and intobores 18 and 20 of nozzles 21 and 23, respectively. Melt is injected outof nozzles 21 and 23 and into cavity 5 (where the part is formed) whichis formed by mold plates 25 and 27. Although a multi-gate single-cavitysystem is shown, the invention is not limited to this type of system,and is also applicable to, for example, multi-cavity systems, asdiscussed in greater detail below.

The injection nozzles 21 and 23 are received in respective wells 28 and29 formed in the mold plate 27. The nozzles 21 and 23 are each seated insupport rings 31 and 33. The support rings serve to align the nozzleswith the gates 7 and 9 and insulate the nozzles from the mold. Themanifold 15 sits atop the rear end of the nozzles and maintains sealingcontact with the nozzles via compression forces exerted on the assemblyby clamps (not shown) of the injection molding machine. An O-ring 36 isprovided to prevent melt leakage between the nozzles and the manifold. Adowel 73 centers the manifold on the mold plate 27. Dowels 32 and 34prevent the nozzle 23 and support ring 33, respectively, from rotatingwith respect to the mold 27.

The nozzles also include a heater 35 (FIG. 2). Although an electric bandheater is shown, other heaters may be used. Furthermore, heat pipes (forexample those disclosed in U.S. Pat. No. 4,389,002) may be disposed ineach nozzle and used alone or in conjunction with heater 35. The heateris used to maintain the melt material at its processing temperature upto the gates 7 and 9. The nozzles 21 and 23 also include an insert 37and a tip 39. The insert can be made of a material (for exampleberyllium copper) having high thermal conductivity in order to maintainthe melt at its processing temperature up to the gate by imparting heatto the melt from the heater 35. The tip 39 is used to form a seal withthe mold plate 27 and is preferably a material (for example titaniumalloy or stainless steel) having low thermal conductivity so as toreduce heat transfer from the nozzle to the mold.

A valve pin 41 having a head 43 is used to control the rate of flow ofthe melt material to the respective gates 7 and 9. The valve pinreciprocates through the manifold. A valve pin bushing 44 is provided toprevent melt from leaking along stem 102 of the valve pin. The valve pinbushing is held in place by a threadably mounted cap 46. The valve pinis opened at the beginning of the injection cycle and closed at the endof the cycle. During the cycle, the valve pin can assume intermediatepositions between the fully open and closed positions, in order todecrease or increase the rate of flow of the melt. The head includes atapered portion 45 that forms a gap 81 with a surface 47 of the bore 19of the manifold. Increasing or decreasing the size of the gap bydisplacing the valve pin correspondingly increases or decreases the flowof melt material to the gate. When the valve pin is closed the taperedportion 45 of the valve pin head contacts and seals with the surface 47of the bore of the manifold.

FIG. 2 shows the head of the valve pin in a Phantom dashed line in theclosed position and a solid line in the fully opened position in whichthe melt is permitted to flow at a maximum rate. To reduce the flow ofmelt, the pin is retracted away from the gate by an actuator 49, tothereby decrease the width of the gap 81 between the valve pin and thebore 19 of the manifold.

The actuator 49 (for example, the type disclosed in application Ser. No.08/874,962) is mounted in a clamp plate 51 which covers the injectionmolding system 1. The actuator 49 is a hydraulic actuator, however,pneumatic or electronic actuators can be used. The actuator 49 includesa hydraulic circuit that includes a movable piston 53 in which the valvepin 41 is threadably mounted at 55. Thus, as the piston 53 moves, thevalve pin 41 moves with it. The actuator 49 includes hydraulic lines 57and 59 which are controlled by servo valves 1 and 2. Hydraulic line 57is energized to move the valve pin 41 toward the gate to the openposition, and hydraulic line 59 is energized to retract the valve pinaway from the gate toward the close position. An actuator cap 61 limitslongitudinal movement in the vertical direction of the piston 53.O-rings 63 provide respective seals to prevent hydraulic fluid fromleaking out of the actuator. The actuator body 65 is mounted to themanifold via screws 67.

A pressure transducer 69 is used to sense the pressure in the manifoldbore 19 downstream of the valve pin head 43. In operation, theconditions sensed by the pressure transducer 69 associated with eachnozzle are fed back to a control system that includes controllers PID 1and PID 2 and a CPU shown schematically in FIG. 1. The CPU executes aPID (proportional, integral, derivative) algorithm which compares thesensed pressure (at a given time) from the pressure transducer to aprogrammed target pressure (for the given time). The CPU instructs thePID controller to adjust the valve pin using the actuator 49 in order tomirror the target pressure for that given time. In this way a programmedtarget pressure profile for an injection cycle for a particular part foreach gate 7 and 9 can be followed.

Although in the disclosed embodiment the sensed condition is pressure,other sensed conditions can be used which relate to melt flow rate. Forexample, the position of the valve pin or the load on the valve pincould be the sensed condition. If so, a position sensor or load sensor,respectively, could be used to feed back the sensed condition to the PIDcontroller. In the same manner as explained above, the CPU would use aPID algorithm to compare the sensed condition to a programmed targetposition profile or load profile for the particular gate to the moldcavity, and adjust the valve pin accordingly.

Melt flow rate is directly related to the pressure sensed in bore 19.Thus, using the controllers PID 1 and PID 2, the rate at which the meltflows into the gates 7 and 9 can be adjusted during a given injectionmolding cycle, according to the desired pressure profile. The pressure(and rate of melt flow) is decreased by retracting the valve pin anddecreasing the width of the gap 81 between the valve pin and themanifold bore, while the pressure (and rate of melt flow) is increasedby displacing the valve pin toward the gate 9, and increasing the widthof the gap 81. The PID controllers adjust the position of the actuatorpiston 51 by sending instructions to servo valves 1 and 2.

By controlling the pressure in a single cavity system (as shown inFIG. 1) it is possible to adjust the location and shape of the weld lineformed when melt flow 75 from gate 7 meets melt flow 77 from gate 9 asdisclosed in U.S. Pat. No. 5,556,582. However, the invention also isuseful in a multi-cavity system. In a multi-cavity system the inventioncan be used to balance fill rates and packing profiles in the respectivecavities. This is useful, for example, when molding a plurality of likeparts in different cavities. In such a system, to achieve a uniformityin the parts, the fill rates and packing profiles of the cavities shouldbe as close to identical as possible. Using the same programmed pressureprofile for each nozzle, unpredictable fill rate variations from cavityto cavity are overcome, and consistently uniform parts are produced fromeach cavity.

Another advantage of the present invention is seen in a multi-cavitysystem in which the nozzles are injecting into cavities which formdifferent sized parts that require different fill rates and packingprofiles. In this case, different pressure profiles can be programmedfor each respective controller of each respective cavity. Still anotheradvantage is when the size of the cavity is constantly changing, i.e.,when making different size parts by changing a mold insert in which thepart is formed. Rather than change the hardware (e.g., the nozzle)involved in order to change the fill rate and packing profile for thenew part, a new program is chosen by the user corresponding to the newpart to be formed.

The embodiment of FIGS. 1 and 2 has the advantage of controlling therate of melt flow away from the gate inside manifold 15 rather than atthe gates 7 and 9. Controlling the melt flow away from the gate enablesthe pressure transducer to be located away from the gate (in FIGS. 1-5).In this way, the pressure transducer does not have to be placed insidethe mold cavity, and is not susceptible to pressure spikes which canoccur when the pressure transducer is located in the mold cavity or nearthe gate. Pressure spikes in the mold cavity result from the valve pinbeing closed at the gate. This pressure spike could cause an unintendedresponse from the control system, for example, an opening of the valvepin to reduce the pressure when the valve pin should be closed.

Avoidance of the effects of a pressure spike resulting from closing thegate to the mold makes the control system behave more accurately andpredictably. Controlling flow away from the gate enables accuratecontrol using only a single sensed condition (e.g., pressure) as avariable. The '582 patent disclosed the use of two sensed conditions(valve position and pressure) to compensate for an unintended responsefrom the pressure spike. Sensing two conditions resulted in a morecomplex control algorithm (which used two variables) and morecomplicated hardware (pressure and position sensors).

Another advantage of controlling the melt flow away from the gate is theuse of a larger valve pin head 43 than would be used if the valve pinclosed at the gate. A larger valve pin head can be used because it isdisposed in the manifold in which the melt flow bore 19 can be madelarger to accommodate the larger valve pin head. It is generallyundesirable to accommodate a large size valve pin head in the gate areawithin the end of the nozzle 23, tip 39 and insert 37. This is becausethe increased size of the nozzle, tip and insert in the gate area couldinterfere with the construction of the mold, for example, the placementof water lines within the mold which are preferably located close to thegate. Thus, a larger valve pin head can be accommodated away from thegate.

The use of a larger valve pin head enables the use of a larger surface45 on the valve pin head and a larger surface 47 on the bore to form thecontrol gap 81. The more “control” surface (45 and 47) and the longerthe “control” gap (81) —the more precise control of the melt flow rateand pressure can be obtained because the rate of change of melt flow permovement of the valve pin is less. In FIGS. 1-3 the size of the gap andthe rate of melt flow is adjusted by adjusting the width of the gap,however, adjusting the size of the gap and the rate of material flow canalso be accomplished by changing the length of the gap, i.e., the longerthe gap the more flow is restricted. Thus, changing the size of the gapand controlling the rate of material flow can be accomplished bychanging the length or width of the gap.

The valve pin head includes a middle section 83 and a forward coneshaped section 95 which tapers from the middle section to a point 85.This shape assists in facilitating uniform melt flow when the melt flowspast the control gap 81. The shape of the valve pin also helpseliminates dead spots in the melt flow downstream of the gap 81.

FIG. 3 shows another aspect in which a plug 87 is inserted in themanifold 15 and held in place by a cap 89. A dowel 86 keeps the plugfrom rotating in the recess of the manifold that the plug is mounted.The plug enables easy removal of the valve pin 41 without disassemblingthe manifold, nozzles and mold. When the plug is removed from themanifold, the valve pin can be pulled out of the manifold where the plugwas seated since the diameter of the recess in the manifold that theplug was in is greater than the diameter of the valve pin head at itswidest point. Thus, the valve pin can be easily replaced withoutsignificant downtime.

FIGS. 4 and 5 show additional alternative embodiments of the inventionin which a threaded nozzle style is used instead of a support ringnozzle style. In the threaded nozzle style, the nozzle 23 is threadeddirectly into manifold 15 via threads 91. Also, a coil heater 93 is usedinstead of the band heater shown in FIGS. 1-3. The threaded nozzle styleis advantageous in that it permits removal of the manifold and nozzles(21 and 23) as a unitary element. There is also less of a possibility ofmelt leakage where the nozzle is threaded on the manifold. The supportring style (FIGS. 1-3) is advantageous in that one does not need to waitfor the manifold to cool in order to separate the manifold from thenozzles. FIG. 5 also shows the use of the plug 87 for convenient removalof valve pin 41.

FIGS. 6-10 show an alternative embodiment of the invention in which a“forward” shutoff is used rather than a retracted shutoff as shown inFIGS. 1-5. In the embodiment of FIGS. 6 and 7, the forward cone-shapedtapered portion 95 of the valve pin head 43 is used to control the flowof melt with surface 97 of the inner bore 20 of nozzle 23. An advantageof this arrangement is that the valve pin stem 102 does not restrict theflow of melt as in FIGS. 1-5. As seen in FIGS. 1-5, the clearance 100between the stem 102 and the bore 19 of the manifold is not as great asthe clearance 100 in FIGS. 6 and 7. The increased clearance 100 in FIGS.6-7 results in a lesser pressure drop and less shear on the plastic.

In FIGS. 6 and 7 the control gap 98 is formed by the front cone-shapedportion 95 and the surface 97 of the bore 20 of the rear end of thenozzle 23. The pressure transducer 69 is located downstream of thecontrol gap—thus, in FIGS. 6 and 7, the nozzle is machined toaccommodate the pressure transducer as opposed to the pressuretransducer being mounted in the manifold as in FIGS. 1-5.

FIG. 7 shows the valve pin in solid lines in the open position andPhantom dashed lines in the closed position. To restrict the melt flowand thereby reduce the melt pressure, the valve pin is moved forwardfrom the open position towards surface 97 of the bore 20 of the nozzlewhich reduces the width of the control gap 98. To increase the flow ofmelt the valve pin is retracted to increase the size of the gap 98.

The rear 45 of the valve pin head 43 remains tapered at an angle fromthe stem 102 of the valve pin 41. Although the surface 45 performs nosealing function in this embodiment, it is still tapered from the stemto facilitate even melt flow and reduce dead spots.

As in FIGS. 1-5, pressure readings are fed back to the control system(CPU and PID controller), which can accordingly adjust the position ofthe valve pin 41 to follow a target pressure profile. The forwardshut-off arrangement shown in FIGS. 6 and 7 also has the advantages ofthe embodiment shown in FIGS. 1-5 in that a large valve pin head 43 isused to create a long control gap 98 and a large control surface 97. Asstated above, a longer control gap and greater control surface providesmore precise control of the pressure and melt flow rate.

FIGS. 8 and 9 show a forward shutoff arrangement similar to FIGS. 6 and7, but instead of shutting off at the rear of the nozzle 23, theshut-off is located in the manifold at surface 101. Thus, in theembodiment shown in FIGS. 8 and 9, a conventional threaded nozzle 23 maybe used with a manifold 15, since the manifold is machined toaccommodate the pressure transducer 69 as in FIGS. 1-5. A spacer 88 isprovided to insulate the manifold from the mold. This embodiment alsoincludes a plug 87 for easy removal of the valve pin head 43.

FIG. 10 shows an alternative embodiment of the invention in which aforward shutoff valve pin head is shown as used in FIGS. 6-9. However,in this embodiment, the forward cone-shaped taper 95 on the valve pinincludes a raised section 103 and a recessed section 104. Ridge 105shows where the raised portion begins and the recessed section ends.Thus, a gap 107 remains between the bore 20 of the nozzle through whichthe melt flows and the surface of the valve pin head when the valve pinis in the closed position. Thus, a much smaller surface 109 is used toseal and close the valve pin. The gap 107 has the advantage in that itassists opening of the valve pin which is subjected to a substantialforce F from the melt when the injection machine begins an injectioncycle. When injection begins melt will flow into gap 107 and provide aforce component F1 that assists the actuator in retracting and openingthe valve pin. Thus, a smaller actuator, or the same actuator with lesshydraulic pressure applied, can be used because it does not need togenerate as much force in retracting the valve pin. Further, the stressforces on the head of the valve pin are reduced.

Despite the fact that the gap 107 performs no sealing function, itswidth is small enough to act as a control gap when the valve pin is openand correspondingly adjust the melt flow pressure with precision as inthe embodiments of FIGS. 1-9.

FIGS. 11 and 12 show an alternative hot-runner system having flowcontrol in which the control of melt flow is still away from the gate asin previous embodiments. Use of the pressure transducer 69 and PIDcontrol system is the same as in previous embodiments. In thisembodiment, however, the valve pin 41 extends past the area of flowcontrol via extension 110 to the gate. The valve pin is shown in solidlines in the fully open position and in Phantom dashed lines in theclosed position. In addition to the flow control advantages away fromthe gate described above, the extended valve pin has the advantage ofshutting off flow at the gate with a tapered end 112 of the valve pin41.

Extending the valve pin to close the gate has several advantages. First,it shortens injection cycle time. In previous embodiments thermal gatingis used. In thermal gating, plastication does not begin until the partfrom the previous cycle is ejected from the cavity. This preventsmaterial from exiting the gate when the part is being ejected. Whenusing a valve pin, however, plastication can be performed simultaneouslywith the opening of the mold when the valve pin is closed, thusshortening cycle time by beginning plastication sooner. Using a valvepin can also result in a smoother gate surface on the part.

The flow control area is shown enlarged in FIG. 12. In solid lines thevalve pin is shown in the fully open position in which maximum melt flowis permitted. The valve pin includes a convex surface 114 that tapersfrom edge 128 of the stem 102 of the valve pin 41 to a throat area 116of reduced diameter. From throat area 116, the valve pin expands indiameter in section 118 to the extension 110 which extends in a uniformdiameter to the tapered end of the valve pin.

In the flow control area the manifold includes a first section definedby a surface 120 that tapers to a section of reduced diameter defined bysurface 122. From the section of reduced diameter the manifold channelthen expands in diameter in a section defined by surface 124 to anoutlet of the manifold 126 that communicates with the bore of the nozzle20. FIGS. 11 and 12 show the support ring style nozzle similar to FIGS.1-3. However, other types of nozzles may be used such as, for example, athreaded nozzle as shown in FIG. 8.

As stated above, the valve pin is shown in the fully opened position insolid lines. In FIG. 12, flow control is achieved and melt flow reducedby moving the valve pin 41 forward toward the gate thereby reducing thewidth of the control gap 98. Thus, surface 114 approaches surface 120 ofthe manifold to reduce the width of the control gap and reduce the rateof melt flow through the manifold to the gate.

To prevent melt flow from the manifold bore 19, and end the injectioncycle, the valve pin is moved forward so that edge 128 of the valve pin,i.e., where the stem 102 meets the beginning of curved surface 114, willmove past point 130 which is the beginning of surface 122 that definesthe section of reduced diameter of the manifold bore 19. When edge 128extends past point 130 of the manifold bore melt flow is prevented sincethe surface of the valve stem 102 seals with surface 122 of themanifold. The valve pin is shown in dashed lines where edge 128 isforward enough to form a seal with surface 122. At this position,however, the valve pin is not yet closed at the gate. To close the gatethe valve pin moves further forward, with the surface of the stem 102moving further along, and continuing to seal with, surface 122 of themanifold until the end 112 of the valve pin closes with the gate.

In this way, the valve pin does not need to be machined to close thegate and the flow bore 19 of the manifold simultaneously, since stem 102forms a seal with surface 122 before the gate is closed. Further,because the valve pin is closed after the seal is formed in themanifold, the valve pin closure will not create any unwanted pressurespikes. Likewise, when the valve pin is opened at the gate, the end 112of the valve pin will not interfere with melt flow, since once the valvepin is retracted enough to permit melt flow through gap 98, the valvepin end 112 is a predetermined distance from the gate. The valve pincan, for example, travel 6 mm. from the fully open position to where aseal is first created between stem 102 and surface 122, and another 6mm. to close the gate. Thus, the valve pin would have 12 mm. of travel,6 mm. for flow control, and 6 mm. with the flow prevented to close thegate. Of course, the invention is not limited to this range of travelfor the valve pin, and other dimensions can be used.

FIGS. 13-15 show another alternative hot runner system having flowcontrol in which the control of material flow is away from the gate.Like the embodiment shown in FIGS. 11 and 12, the embodiment shown inFIGS. 13-15 also utilizes an extended valve pin design in which thevalve pin closes the gate after completion of material flow. Unlike theembodiment of FIGS. 11 and 12, however, flow control is performed usinga “reverse taper” pin design, similar to the valve pin design shown inFIGS. 1-5.

The valve pin 200 includes a reverse tapered control surface 205 forforming a gap 207 with a surface 209 of the manifold (see FIG. 14). Theaction of displacing the pin 200 away from the gate 211 reduces the sizeof the gap 207. Consequently, the rate of material flow through bores208 and 214 of nozzle 215 and manifold 231, respectively, is reduced,thereby reducing the pressure measured by the pressure transducer 217.Although only one nozzle 215 is shown, manifold 231 supports two or morelike nozzle arrangements shown in FIGS. 13-15, each nozzle for injectinginto a single or multiple cavities.

The valve pin 200 reciprocates by movement of piston 223 disposed in anactuator body 225. This actuator is described in co-pending applicationSer. No. 08/874,962. As disclosed in that application, the use of thisactuator enables easy access to valve pin 200 in that the actuator body225 and piston 223 can be removed from the manifold and valve pin simpleby releasing retaining ring 240.

The reverse closure method offers an advantage over the forward closuremethod shown in FIGS. 6-9, 11 and 12, in that the action of the valvepin 200 moving away from the gate acts to displace material away fromthe gate, thereby assisting in the desired effect of decreasing flowrate and pressure.

In the forward closure method shown in FIGS. 6-9, forward movement ofthe pin is intended to reduce the control gap between the pin and themanifold (or nozzle) bore surface to thereby decrease flow rate andpressure. However, forward movement of the pin also tends to displacematerial toward the gate and into the cavity, thereby increasingpressure, working against the intended action of the pin to restrictflow.

Like the embodiment shown in FIGS. 6-9, and the embodiment shown inFIGS. 11 and 12, movement of the valve pin away from the gate is alsointended to increase the flow rate and pressure. This movement, however,also tends to displace material away from the gate and decreasepressure. Accordingly, although either design can be used, the reversetaper design has been found to give better control stability in trackingthe target pressure.

The embodiment shown in FIGS. 13-15 also includes a tip heater 219disposed about an insert 221 in the nozzle. The tip heater providesextra heat at the gate to keep the material at its processingtemperature. The foregoing tip heater is described in U.S. Pat. No.5,871,786, entitled “Tip Heated Hot Runner Nozzle.” Heat pipes 242 arealso provided to conduct heat uniformly about the injection nozzle 215and to the tip area. Heat pipes such as these are described in U.S. Pat.No. 4,389,002.

FIGS. 13-15 show the valve pin in three different positions. FIG. 13represents the position of the valve pin at the start of an injectioncycle. Generally, an injection cycle includes: 1) an injection periodduring which substantial pressure is applied to the melt stream from theinjection molding machine to inject the material in the mold cavity; 2)a reduction of the pressure from the injection molding machine in whichmelt material is packed into the mold cavity at a relatively constantpressure; and 3) a cooling period in which the pressure decreases tozero and the article in the mold solidifies.

Just prior to the start of injection, tapered control surface 205 is incontact with manifold surface 209 to prevent any material flow. At thestart of injection the pin 200 will be opened to allow material flow. Tostart the injection cycle the valve pin 200 is displaced toward the gateto permit material flow, as shown in FIG. 14. (Note: for someapplications, not all the pins will be opened initially, for some gatespin opening will be varied to sequence the fill into either a singlecavity or multiple cavities). FIG. 15 shows the valve pin at the end ofthe injection cycle after pack. The part is ejected from the mold whilethe pin is in the position shown in FIG. 15.

As in previous embodiments, pin position will be controlled by acontroller 210 based on pressure readings fed to the controller frompressure sensor 217. In a preferred embodiment, the controller is aprogrammable controller, or “PLC,” for example, model number 90-30PLCmanufactured by GE-Fanuc. The controller compares the sensed pressure toa target pressure and adjusts the position of the valve pin via servovalve 212 to track the target pressure, displacing the pin forwardtoward the gate to increase material flow (and pressure) and withdrawingthe pin away from the gate to decrease material flow (and pressure). Ina preferred embodiment, the controller performs this comparison andcontrols pin position according to a PID algorithm. Furthermore, as analternative, valve 212 can also be a high speed proportional valve.

The controller also performs these functions for the other injectionnozzles (not shown) coupled to the manifold 231. Associated with each ofthese nozzles is a valve pin or some type of control valve to controlthe material flow rate, a pressure transducer, an input device forreading the output signal of the pressure transducer, means for signalcomparison and PID calculation (e.g., the controller 210), means forsetting, changing and storing a target profile (e.g., interface 214), anoutput means for controlling a servo valve or proportional valve, and anactuator to move the valve pin. The actuator can be pneumatic, hydraulicor electric. The foregoing components associated with each nozzle tocontrol the flow rate through each nozzle are called a control zone oraxis of control. Instead of a single controller used to control allcontrol zones, alternatively, individual controllers can be used in asingle control zone or group of control zones.

An operator interface 214, for example, a personal computer, is used toprogram a particular target pressure profile into controller 210.Although a personal computer is used, the interface 214 can be anyappropriate graphical or alpha numeric display, and could be directlymounted to the controller. As in previous embodiments, the targetprofile is selected for each nozzle and gate associated therewith bypre-selecting a target profile (preferably including at least parametersfor injection pressure, injection time, pack pressure and pack time),programming the target profile into controller 210, and running theprocess.

In the case of a multicavity application in which different parts arebeing produced in independent cavities associated with each nozzle (a“family tool” mold), it is preferable to create each target profileseparately, since different shaped and sized cavities can have differentprofiles which produce good parts.

For example, in a system having a manifold with four nozzles coupledthereto for injecting into four separate cavities, to create a profilefor a particular nozzle and cavity, three of the four nozzles are shutoff while the target profile is created for the fourth. Three of thefour nozzles are shut off by keeping the valve pins in the positionshown in FIGS. 13 or 15 in which no melt flow is permitted into thecavity.

To create the target profile for the particular nozzle and cavityassociated therewith, the injection molding machine is set at maximuminjection pressure and screw speed, and parameters relating to theinjection pressure, injection time, pack pressure and pack time are seton the controller 210 at values that the molder estimates will generategood parts based on part size, shape, material being used, experience,etc. Injection cycles are run for the selected nozzle and cavity, withalterations being made to the above parameters depending on thecondition of the part being produced. When satisfactory parts areproduced, the profile that produced the satisfactory parts is determinedfor that nozzle and cavity associated therewith.

This process is repeated for all four nozzles (keeping three valve pinsclosed while the selected nozzle is profiled) until target profiles areascertained for each nozzle and cavity associated therewith. Preferably,the acceptable target profiles are stored in computer member, forexample, on a file stored in interface 214 and used by controller 210for production. The process can then be run for all four cavities usingthe four particularized profiles.

Of course, the foregoing process of profile creation is not limited touse with a manifold having four nozzles, but can be used with any numberof nozzles. Furthermore, although it is preferable to profile one nozzleand cavity at a time (while the other nozzles are closed) in a “familytool” mold application, the target profiles can also be created byrunning all nozzles simultaneously, and similarly adjusting each nozzleprofile according the quality of the parts produced. This would bepreferable in an application where all the nozzles are injecting intolike cavities, since the profiles should be similar, if not the same,for each nozzle and cavity associated therewith.

In single cavity applications (where multiple nozzles from a manifoldare injecting into a single cavity), the target profiles would also becreated by running the nozzles at the same time and adjusting theprofiles for each nozzle according to the quality of the part beingproduced. The system can also be simplified without using interface 214,in which each target profile can be stored on a computer readable mediumin controller 210, or the parameters can be set manually on thecontroller.

FIG. 14 shows the pin position in a position that permits material flowduring injection and/or pack. As described above, when the targetprofile calls for an increase in pressure, the controller will cause thevalve pin 200 to move forward to increase gap 207, which increasesmaterial flow, which increases the pressure sensed by pressuretransducer 217. If the injection molding machine is not providingadequate pressure (i.e., greater than the target pressure), however,moving the pin forward will not increase the pressure sensed bytransducer 217 enough to reach the target pressure, and the controllerwill continue to move the pin forward calling for an increase inpressure. This could lead to a loss of control since moving the pinfurther forward will tend to cause the head 227 of the valve pin toclose the gate and attenuate material flow through and about the gate.

Accordingly, to prevent loss of control due to inadequate injectionpressure, the output pressure of the injection molding machine can bemonitored to alert an operator when the pressure drops below aparticular value relative to the target pressure. Alternatively, theforward stroke of the valve pin (from the position in FIG. 13 to theposition in FIG. 14) can be limited during injection and pack. In apreferred embodiment, the pin stroke is limited to approximately 4millimeters. Greater or smaller ranges of pin movement can be useddepending on the application. If adequate injection pressure is not aproblem, neither of these safeguards is necessary.

To prevent the movement of the valve pin too far forward duringinjection and pack several methods can be used. For example, a controllogic performed by the controller 210 can be used in which the outputsignal from the controller to the servo valve is monitored. Based onthis signal, an estimate of the valve pin position is made.

If the valve pin position exceeds a desired maximum, for example, 4millimeters, then the forward movement of the pin is halted, or reversedslightly away from the gate. At the end of the injection cycle, thecontrol logic is no longer needed, since the pin is moved to the closedposition of FIG. 15 and attenuation of flow is no longer a concern.Thus, at the end of the pack portion of the injection cycle, a signal issent to the servo valve to move the pin forward to the closed positionof FIG. 15.

Other methods and apparatus for detecting and limiting forwarddisplacement of the valve pin 200 can be used during injection and pack.For example, the pressure at the injection molding machine nozzle can bemeasured to monitor the material pressure supplied to the manifold. Ifthe input pressure to the manifold is less than the target pressure, orless than a specific amount above the target pressure, e.g., 500 p.s.i.,an error message is generated.

Another means for limiting the forward movement of the pin is amechanical or proximity switch which can be used to detect and limit thedisplacement of the valve pin towards the gate instead of the controllogic previously described. The mechanical or proximity switch indicateswhen the pin travels beyond the control range (for example, 4millimeters). If the switch changes state, the direction of the pintravel is halted or reversed slightly to maintain the pin within thedesired range of movement.

Another means for limiting the forward movement of the pin is a positionsensor, for example, a linear voltage differential transformer (LVDT)that is mounted onto the pin shaft to give an output signal proportionalto pin distance traveled. When the output signal indicates that the pintravels beyond the control range, the movement is halted or reversedslightly.

Still another means for limiting the forward movement of the pin is anelectronic actuator. An electronic actuator is used to move the pininstead of the hydraulic or pneumatic actuator shown in FIGS. 13-15. Anexample of a suitable electronic actuator is shown in co-pending U.S.Ser. No. 09/187,974. Using an electronic actuator, the output signal tothe servo valve motor can be used to estimate pin position, or anencoder can be added to the motor to give an output signal proportionalto pin position. As with previous options, if the pin position travelsbeyond the control range, then the direction is reversed slightly or theposition maintained.

At the end of the pack portion of the injection cycle, the valve pin 200is moved all the way forward to close off the gate as shown in FIG. 15.In the foregoing example, the full stroke of the pin (from the positionin FIG. 13 to the position in FIG. 15) is approximately 12 millimeters.Of course, different ranges of movement can be used depending on theapplication.

The gate remains closed until just prior to the start of the nextinjection cycle when it is opened and moved to the position shown inFIG. 13. While the gate is closed, as shown in FIG. 15, the injectionmolding machine begins plastication for the next injection cycle as thepart is cooled and ejected from the mold.

FIG. 16 shows time versus pressure graphs (235, 237, 239, 241) of thepressure detected by four pressure transducers associated with fournozzles mounted in manifold block 231. The four nozzles aresubstantially similar to the nozzle shown in FIGS. 13-15, and includepressure transducers coupled to the controller 210 in the same manner aspressure transducer 217.

The graphs of FIGS. 16 (a-d) are generated on the user interface 214 sothat a user can observe the tracking of the actual pressure versus thetarget pressure during the injection cycle in real time, or after thecycle is complete. The four different graphs of FIG. 16 show fourindependent target pressure profiles (“desired”) emulated by the fourindividual nozzles. Different target profiles are desirable to uniformlyfill different sized individual cavities associated with each nozzle, orto uniformly fill different sized sections of a single cavity. Graphssuch as these can be generated with respect to any of the previousembodiments described herein.

The valve pin associated with graph 235 is opened sequentially at 0.5seconds after the valves associated with the other three graphs (237,239 and 241 ) were opened at 0.00 seconds. Referring back to FIGS.13-15, just before opening, the valve pins are in the position shown inFIG. 13, while at approximately 6.25 seconds at the end of the injectioncycle all four valve pins are in the position shown in FIG. 15. Duringinjection (for example, 0.00 to 1.0 seconds in FIG. 16b) and pack (forexample, 1.0 to 6.25 seconds in FIG. 16b) portions of the graphs, eachvalve pin is controlled to a plurality of positions to alter thepressure sensed by the pressure transducer associated therewith to trackthe target pressure.

Through the user interface 214, target profiles can be designed, andchanges can be made to any of the target profiles using standardwindows-based editing techniques. The profiles are then used bycontroller 210 to control the position of the valve pin. For example,FIG. 17 shows an example of a profile creation and editing screen icon300 generated on interface 214.

Screen icon 300 is generated by a windows-based application performed oninterface 214. Alternatively, this icon could be generated on aninterface associated with controller 210. Screen icon 300 provides auser with the ability to create a new target profile or edit an existingtarget profile for any given nozzle and cavity associated therewith.Screen icon 300 and the profile creation text techniques describedherein are described with reference to FIGS. 13-15, although they areapplicable to all embodiments described herein.

A profile 310 includes (x, y) data pairs, corresponding to time values320 and pressure values 330 which represent the desired pressure sensedby the pressure transducer for the particular nozzle being profiled. Thescreen icon shown in FIG. 17 is shown in a “basic” mode in which alimited group of parameters are entered to generate a profile. Forexample, in the foregoing embodiment, the “basic” mode permits a user toinput start time displayed at 340, maximum fill pressure displayed at350 (also known as injection pressure), the start of pack time displayedat 360, the pack pressure displayed at 370, and the total cycle timedisplayed at 380.

The screen also allows the user to select the particular valve pin theyare controlling displayed at 390, and name the part being moldeddisplayed at 400. Each of these parameters can be adjusted independentlyusing standard windows-based editing techniques such as using a cursorto actuate up/down arrows 410, or by simply typing in values on akeyboard. As these parameters are entered and modified, the profile willbe displayed on a graph 420 according to the parameters selected at thattime.

By clicking on a pull-down menu arrow 391, the user can select differentnozzle valves in order to create, view or edit a profile for theselected nozzle valve and cavity associated therewith. Also, a part name400 can be entered and displayed for each selected nozzle valve.

The newly edited profile can be saved in computer memory individually,or saved as a group of profiles for a group of nozzles that inject intoa particular single or multi-cavity mold. The term “recipe” is used todescribe a group of profiles for a particular mold and the name of theparticular recipe is displayed at 430 on the screen icon.

To create a new profile or edit an existing profile, first the userselects a particular nozzle valve of the group of valves for theparticular recipe group being profiled. The valve selection is displayedat 390. The user inputs an alpha/numeric name to be associated with theprofile being created, for family tool molds this may be called a partname displayed at 400. The user then inputs a time displayed at 340 tospecify when injection starts. A delay can be with particular valve pinsto sequence the opening of the valve pins and the injection of meltmaterial into different gates of a mold.

The user then inputs the fill (injection) pressure displayed at 35. Inthe basic mode, the ramp from zero pressure to max fill pressure is afixed time, for example, 0.3 seconds. The user next inputs the startpack time to indicate when the pack phase of the injection cycle starts.The ramp from the filling phase to the packing phase is also fixed timein the basic mode, for example, 0.3 seconds.

The final parameter is the cycle time which is displayed at 380 in whichthe user specifies when the pack phase (and the injection cycle) ends.The ramp from the pack phase to zero pressure will be instantaneous whena valve pin is used to close the gate, as in the embodiment of FIG. 13,or slower in a thermal gate (see FIG. 1) due to the residual pressure inthe cavity which will decay to zero pressure once the part solidifies inthe mold cavity.

User input buttons 415 through 455 are used to save and load targetprofiles. Button 415 permits the user to close the screen. When thisbutton is clicked, the current group of profiles will take effect forthe recipe being profiled. Cancel button 425 is used to ignore currentprofile changes and revert back to the original profiles and close thescreen. Read Trace button 435 is used to load an existing and savedtarget profile from memory. The profiles can be stored in memorycontained in the interface 215 or the controller 210. Save trace button440 is used to save the current profile. Read group button 445 is usedto load an existing recipe group. Save group button 450 is used to savethe current group of target profiles for a group of nozzle valve pins.The process tuning button 455 allows the user to change the PID settings(for example, the gains) for a particular nozzle valve in a controlzone. Also displayed is a pressure range 465 for the injection moldingapplication.

Button 460 permits the user to toggle to an “advanced” mode profilecreation and editing screen. The advanced profile creation and editingscreen is shown in FIG. 18. The advanced mode allows a greater number ofprofile points to be inserted, edited, or deleted than the basic mode.As in the basic mode, as the profile is changed, the resulting profileis displayed.

The advanced mode offers greater profitability because the user canselect values for individual time and pressure data pairs. As shown inthe graph 420, the profile 470 displayed is not limited to a singlepressure for fill and pack, respectively, as in the basic mode. In theadvanced mode, individual (x, y) data pairs (time and pressure) can beselected anywhere during the injection cycle.

To create and edit a profile using advanced mode, the user can select aplurality of times during the injection cycle (for example 16 differenttimes), and select a pressure value for each selected time. Usingstandard windows-based editing techniques (arrows 475) the user assignsconsecutive points along the profile (displayed at 478), particular timevalues displayed at 480 and particular pressure values displayed at 485.

The next button 490 is used to select the next point on the profile forediting. Prev button 495 is used to select the previous point on theprofile for editing. Delete button 500 is used for deleting thecurrently selected point. When the delete button is used the twoadjacent points will be redrawn showing one straight line segment.

The add button 510 is used to add a new point after the currentlyselected point in which time and pressure values are entered for the newpoint. When the add button is used the two adjacent points will beredrawn showing two segments connecting to the new point.

FIGS. 19-23 show another alternative embodiment of an injection moldingsystem. The system includes a manifold 515 having a plurality of nozzles520 coupled thereto for injecting melt material into a plurality ofcavities 525. Alternatively, the nozzles can also inject into a singlecavity. In FIG. 19, only one nozzle 520 is shown but the followingdescription applies to all nozzles coupled to manifold 515.

As in previous embodiments, each nozzle in the system includes apressure transducer 530 associated therewith for sensing the pressure ofthe melt material in the manifold which thereby gives an indication ofrate of meltflow through nozzle 520 and into cavity 525 with respect toeach injection molding nozzle. Mold cavity 525 is formed by mold halves526 and 527, which are separated to eject the molded part formed incavity 525 after the injection cycle. As in previous embodiments, thepressure transducer can also be located in the nozzle, the manifold, orthe cavity.

As in previous embodiments, a controller 535 receives signals frompressure transducers 530 coupled to each nozzle 520 (only one of whichis shown). The controller 535 controls solenoid valve 540 which controlsthe movement of a piston in actuator 545 which is coupled to and acts toreciprocate the valve pin 550 to open and close gate 555 to cavity 525.

The controller also sends a signal to servo valve 560A which controlsactuator 560 which in turn controls the movement of a ram 565, andfurther controls solenoid valve 570 which is coupled to another actuator575 which controls a valve 580 which is adapted to open and close amanifold channel 585 which leads to nozzle 520. Each injection nozzlecoupled to manifold 515 (not shown) includes the foregoing actuators545, 575 and 560 and ram 565 and solenoid valves 540 and 570 and servovalve 560A associated therewith for controlling flow from each nozzle.

The actuators are mounted in a clamp plate 595 which also includes anopening 600 that receives an inlet bushing 610 threadably mounted to themanifold 515. The inlet bushing 610 receives a nozzle 590 from aninjection molding machine. The injection molding machine can be, forexample, a reciprocating or non-reciprocating extruder. The injectionmolding machine nozzle 590 feeds melt material into the central bushing610 into a central channel 620 which branches off via a plurality ofchannels 585 and 630 (and others not shown) to a corresponding pluralityof injection molding nozzles 520.

The foregoing embodiment is similar to previous embodiments in thatpressure transducer 530 is used to measure pressure indicative of flowrate of melt material into cavity 525 during the injection cycle. (Theactuators described herein are hydraulic actuators, however, pneumaticor electric or other types of actuation can also be used.) Also, as inprevious embodiments, a controller 535 compares the pressure sensed bythe pressure transducer to target values of a target profile and issuescontrol signals to increase or decrease pressure to track the targetprofile for each nozzle.

In previous embodiments the controller controlled the position of avalve pin to regulate flow rate independently at each gate duringinjection. The foregoing embodiment also enables the flow rate ofplastic to be controlled independently through each nozzle 520 and eachgate during injection. However, in the embodiment shown in FIGS. 19-23,a valve pin is not used to control flow rate as in previous embodiments.Rather, valve pin 550 is used only to open and close gate 555.

In the foregoing embodiment, ram 565 and well 640 are used to regulatethe flow of melt material through nozzle 520 and into cavity 525 in thefollowing manner.

At the start of the injection cycle, valve gate 555 is closed by valvepin 550 and valve 580 is opened to permit flow through manifold channel585 (see FIG. 20). The injection molding machine nozzle 590 injects meltmaterial through the inlet bushing 610 into the manifold 515, such thatit fills well 640 (see FIG. 20). The valve pin 550 is still in theclosed position while the well 640 is being filled. Ram 565 is in apredetermined adjustable retracted position to permit a specific volumeof melt material to gather in well 640 (see FIG. 21). FIG. 21 shows thesystem ready to inject melt material into cavity 525.

The controller 535 then signals the servo valve 540 to cause actuator545 to retract valve pin 550 and open gate 555, while also signalingservo valve 570 to cause actuator 575 to close valve 580 and shut offmanifold channel 585. Closing valve 580 when injecting into the cavityprevents backflow of material through channel 585. This position isshown in FIG. 22.

The controller then signals actuator 560 to move ram 565 forward toinject material from the well 640 through the nozzle 520 and into thecavity 525. During this time, the controller controls the velocity atwhich the ram moves forward, according to the pressure sensed bypressure transducer 530, in relation to a target pressure profile.Accordingly, if the pressure transducer 530 senses a pressure that isbelow the target pressure for that particular time during the injectioncycle, the controller 535 signals the actuator 560 to increase thevelocity of the ram 565, conversely, if the pressure sensed is greaterthan the target pressure, the controller will control the actuator todecrease the velocity of the ram forward. When the ram reaches itslowermost position, the cavity 525 is full and the gate is closed (seeFIG. 23). Alternatively, ram 565 can be velocity controlled by using alinear transducer to monitor ram position. If so, at the end ofinjection, the ram is not bottomed out, and control can be transferredto the pressure transducer 530 during pack.

As stated above, a reciprocating or non-reciprocating extruder can beused. If a non-reciprocating extruder is used, plastication into themanifold can be continuous, and the valve 580 is used to shut off themanifold channel 585 during injection so that during this time noplastic can flow through the manifold channel. When well 640 is filledwith melt material, plastication in the non-reciprocating extruder canbe stopped until the next cycle.

As in previous embodiments described herein, preferably a PID algorithmis used to control the actuator 560 to track the target profile. Thetarget profile can be created in the same manner as described above withrespect to previous embodiments.

Using the embodiment shown in FIGS. 19-23, the flow rate of plasticthrough each gate is controlled independently. Additionally, the use ofwell 640 enables one to control the specific volume of plastic injectedinto each cavity 525, which leads to part-to-part consistency,especially when molding in multi-cavity applications in which eachcavity 525 is an identical part. By altering the position of ram 565when injecting melt material into well 640, the volume of material inwell 640 can be controlled, thereby controlling the volume of materialinto cavity 525.

FIGS. 24-28 show an alternative embodiment in which a load cell 140 isused to sense the melt pressure acting on the face 142 of valve pin 41.Where possible, reference characters are used that refer to elementscommon to FIG. 1. As in previous embodiments, an actuator 49 is used totranslate the valve pin 41 toward and away from the gate. The actuator49 includes a housing 144 and a piston 146 slidably mounted within thehousing. The actuator is fed by pneumatic or hydraulic lines 148 and150. Other actuators, for example, electrical actuators may also beused.

The valve pin 41 is mounted to the piston 146 so that valve pintranslates through the injection nozzle 23 with movement of the piston.The valve pin is mounted to the piston via a pin 152. The pin 152 isslotted so that a clearance 154 exists in which the valve pin cantranslate with respect to the pin 152 and piston 146. The valve pinbears against a button 156 on the load cell 140. The load cell 140is,mounted via screws 158 to the piston. Thus, as shown in FIG. 26, aforce F2 acting on the valve pin will cause the load button 156 todepress. Excitation voltages or other types of signals which indicatethe proportionate force on the load button 156 are carried through cable160 and fed to a controller 151.

In operation, as seen in FIG. 24, the melt material is injected from aninjection molding machine nozzle 11 into an extended inlet 13 mounted toa manifold 15 through respective injection molding nozzles 21 and 23 andinto mold cavities 162 and 164. In the embodiment shown, a multi-cavitymold is shown in which nozzles 21 and 23 inject melt material to formdifferent size molded parts in cavities 162 and 164, respectively. Asstated above with respect to the embodiment shown in FIG. 1, a moldcavity with multiple gates can be used, or multiple mold cavities withcavities having the same size can be used.

When the valve pin 41 is retracted to permit melt material to beinjected into the cavity 162, the melt pressure will act on the face ofthe valve pin 142 with the resulting force being transmitted through theshaft of the valve pin to the load sensor 140 (see FIGS. 26-27). Thus,the load (F2) sensed by load cell 140 is directly related to the meltflow rate into the melt cavity.

Sheer stresses caused by the melt streaming downward over the valve pinwill tend to reduce the pressure sensed by the load cell but suchstresses are typically less than the nominal load due to the meltpressure. Thus, the resultant force F2 will tend to compress the valvepin toward the load cell, with the possible exception of the initialopening of the valve, and the load cell provides an accurate indicatorof the melt pressure at the gate. If the application results in sheerstresses exceeding F2, the load cell can be pre-loaded to compensate forsuch stresses.

Similar to previous embodiments described above, the signal transmittedthrough cable 160 is compared by controller 151 with a target value of atarget profile and the controller adjusts the position of the valve pinaccordingly to increase or decrease flow rate. In this embodiment, thetarget profile is also a time versus pressure profile, but the pressureis the a result of the force of the pin on the load cell, as opposed toprevious embodiments in which a pressure transducer directly senses theforce of the flow of the melt material. The profile is created insimilar fashion to the embodiments described above: running the processand adjusting the profile until acceptable parts are produced.

The valve pin controls the flow rate through the gate using a taperededge 155 to form a control gap 153 close to the gate. It should benoted, however, that any of the other valve pin designs described hereincan be used with the load cell 140. Accordingly, when the pressuresensed by the load cell is less than the target pressure on the targetprofile, the controller 151 signals the actuator to retract the valvepin to increase the size of the control gap 153 and, consequently, theflow rate. If the pressure sensed by the load cell 140 is greater thanthe target pressure, the controller 151 signals the actuator to displacethe valve pin toward the gate to decrease the size of the control gap153 and consequently, the flow rate.

The use of the load cell has an additional application shown in FIG.27A. In a single cavity multiple gate system it is often desirable toopen gates in a cascading fashion as soon as the flow front of the meltmaterial reaches the gate. When melt material 166 has flowed into thegate area of the valve pin, a force F3 from the melt in the cavity isexerted on the face 142 of the valve pin.

In this way, gates can be sequentially opened in cascading fashion bysensing the force of the melt pressure on the face of the valve pin whenthe valve pin is closed. Given typical gate diameters of 0.2 inches andmelt pressures of 10,000 psi, the resulting force of 300 pounds isreadily measured by available load sensors, since the force of the cellequals the area of the gate times the pressure at the gate. Thus, thismelt detection can then be used to signal the opening of the gate as inthe sequential valve gate. This assures that the gate does not openprematurely.

FIGS. 28A and 28B show an alternative embodiment in which the sheerstress on the valve pin is reduced. The nozzle 21 is designed to includea channel for melt flow 168 and a bore 170 through which the valve pinreciprocates. As such, the flow does not cause any axial sheer stress onthe valve pin and thus reduces errors in pressure sensing. An indent 172is provided in the nozzle 21 so that side load on the valve pin isreduced, i.e., to equalize pressure on both sides of the valve pin. Anadditional benefit to the configuration shown in FIGS. 28A and 28B isthat since the flow of material is away from the valve pin, the valvepin does not “split” the flow of material, which can tend to cause partlines or a flow streak on the molded part.

FIG. 29 shows another alternative embodiment of the present inventionsimilar to FIG. 19. As in FIG. 19, a ram 565 is used to force materialfrom well 640 into cavity 525 at a controlled rate. The rate iscontrolled by signals sent from controller 535 to servo valve 560A,which in turn controls the velocity at which actuator 560 moves ram 565forward.

In FIG. 29, actuator 560 is shown in more detail including piston 564,actuator chamber 566, and hydraulic lines 561 and 562 controlled byservo valve 560A. Energizing hydraulic line 561 and filling chamber 566causes piston 564 and ram 565 to move forward and displace material fromwell 640 through channel 585 and nozzle 520, and into cavity 525. In theembodiment of FIG. 19, the controller controls the rate at which the raminjects material according to signals received by pressure transducer530, compared to a target profile. In the embodiment of FIG. 29,pressure transducer 530 has been removed in favor of pressure transducer563 mounted along hydraulic line 561 which leads to chamber 566. Thepressure transducer 560 senses the hydraulic fluid pressure in line 561and sends a proportional signal to the controller 535. Since thepressure of the hydraulic fluid entering chamber 566 is directly relatedto the rate at which the ram 565 moves forward, and the rate at whichthe ram moves forward is directly related to the rate of material flowinto the cavity 525, the pressure sensed by pressure transducer 560 isdirectly related to the rate of material flow into the cavity 525, andcan be used to control the material flow rate.

Accordingly, as in previous embodiments, a target profile is createdthat has been demonstrated to generate acceptable molded parts. In theembodiment of FIG. 29, however, the target profile represents targetvalues of the hydraulic pressure sensed by pressure transducer 563, asopposed to directly sensing the material pressure. In operation, thecontroller compares the pressure signal sensed from pressure transducer563 to the target pressure profile for gate 555. If the pressure sensedis too low, the controller will increase the hydraulic pressure in line561 (which increases the velocity of the ram which increases flow rateof the material), if the pressure is too high the controller willdecrease the hydraulic pressure (which decreases the velocity of the ramwhich decreases the rate of material flow).

The target pressure profile of the hydraulic fluid will appear similarto a conventional material profile, since the pressure of the hydraulicfluid will rise rapidly during the injection portion of the cycle, leveloff during the pack portion of the cycle, and go to zero pressure ascycle ends the valve pin 550 closes.

Although only one injection nozzle 520 and cavity 525 is shown, there isa like arrangement associated with each injection nozzle of actuators575, 565, 545, as well as solenoid valves 540 and 570 and servo valve560, to independently control the melt flowing from each gate, accordingto the target profile created for that gate. Also, although a singlecavity 525 is shown, each nozzle may inject to multiple cavities or asingle cavity mold. Only a single controller 535, however, is needed tocontrol all the nozzles associated with manifold 515.

Using the foregoing arrangement of FIG. 29, as in previous embodiments,the material flow from each nozzle of the manifold can be controlledindependently.

FIG. 30 shows another alternative embodiment of the present invention.The embodiment of FIG. 30 is substantially the same as the embodimentshown in FIG. 13 with the exception that pressure transducer 217 hasbeen moved from manifold 231 to inside the mold half 650 which, togetherwith mold half 660, forms mold cavity 670 in which the molded part isformed. Accordingly, in this embodiment, the target profile representstarget values of the pressure sensed by pressure transducer 217 insidethe cavity opposite the gate 211.

The operation of the embodiment of FIG. 30 is the same as that describedin the embodiment shown in FIG. 13 in terms of target profile creationand use of valve pin 200 to control the material flow (interface 214 isnot shown FIG. 30 but can be used). However, placing the pressuretransducer in the cavity offers several advantages, for example, in thecavity the pressure transducer 217 is not exposed to the hightemperatures generated by the manifold, as in FIG. 13. Also, thepresence of the pressure transducer in the manifold may slightly disruptmaterial flow in the manifold. Another consideration in choosing whetherto mount the transducer in the mold or in the manifold is whether themold geometry permits the transducer to be mounted in the mold.

FIG. 31 is another alternative embodiment of the present invention thatis similar to FIG. 13 (like reference characters are used whereverpossible). Target profile creation as well as the flow control operationby valve pin 200 is substantially the same as described above. FIG. 31,however, does not include a pressure transducer 217 as shown in FIG. 13to directly sense the flow of melt material into the cavity. Rather,similar to the embodiment shown in FIG. 24, the arrangement shown inFIG. 31 performs flow control by sensing the material pressure F2exerted by the melt material on the valve pin.

In FIG. 24 measuring the load on the valve pin was performed using aload cell 140, however, in FIG. 31, it is performed by pressuretransducers 700 and 710 mounted along hydraulic lines 720 and 730 whichlead to actuator chambers 740 and 750, respectively. Energizing lines720 and 730 and filling actuator chambers 740 and 750, enables axialmovement of piston 223, thereby moving valve pin 200 and affecting theflow rate of the material into the cavity 760 as described above.

Pressure transducers 700 and 710 sense a differential pressure which isdirectly related to the force exerted on valve pin 200, which isdirectly related to the flow rate of the material. For example, when thematerial flow causes a force F2 to act on valve pin 200, the forcerelates up the valve pin to the piston, which in turn tends to increasethe pressure in chamber 740 and line 720 and decrease the pressure inchamber 750 and line 730, directly causing a change in the difference inthe pressures sensed by the transducers 700 and 710. Accordingly, thedifferential pressure is directly related to the flow rate of thematerial into the cavity.

Once an acceptable target profile of differential pressure is developedusing techniques described above, the controller will cause the servovalve 212 to track this target profile by altering the position of thevalve pin to change the flow rate of the material and track thedifferential pressure target profile. For example, if the differentialpressure is too high (e.g., the pressure sensed by transducer 700 ishigher than the pressure sensed by transducer 710 by an amount greaterthan the target differential pressure) the controller will cause servovalve to retract the valve pin to reduce the flow rate, thereby reducingthe force F2 on the valve pin, thereby decreasing the pressure inchamber 740 and line 720, thereby decreasing the pressure sensed bytransducer 700, thereby decreasing the difference in pressure sensed bytransducers 700 and 710. Note, in certain applications the differentialpressure may be negative due to the sheer force of the material on thevalve pin, this however will not affect the controller's ability totrack the target profile.

As in the embodiment shown in FIG. 24, the embodiment shown in FIG. 31offers the advantage that it is not necessary to mount a pressuretransducer in the mold or the manifold. As in all previous embodiments,the embodiment shown in FIG. 31 enables the material flow from eachnozzle attached to the manifold to be independently profileable.

FIG. 32 shows an entire control system arrangement 800 which can be usedwith any of the embodiments described above in FIGS. 1-31. In FIG. 32,the system is shown with the manifold, nozzle and mold arrangement shownin FIG. 1, and like reference characters are used wherever possible.

Similarly to FIG. 1, the control system 800 includes a manifold 15 fordispensing material injected from machine nozzle 11 through injectionmolding nozzles 21 and 23 into a mold cavity 5. As explained above, eachnozzle has a valve pin 41 a and 41 b associated therewith that is usedto independently control the rate of material flow through nozzles 21and 23 and into cavity 5. Servo valves 802 are controlled by controller804 to in turn control actuators 49(a) and 49(b) to alter the respectivepositions of each valve pin according to a target pressure profileassociated with that particular servo-valve, valve pin, injectionnozzle, pressure transducer and gate (herein referred to as a “controlzone”). As explained above, the valve pin of a control zone adjusts theflow rate of the material flowing to the gate of the control zone sothat the pressure read by the pressure transducer in the control zonetracks the target values of pressure in the target profile for thatcontrol zone, throughout the injection cycle.

Real-time control is provided via feedback from pressure transducers69(a) and 69(b) which record material pressure values, feed them backinto controller 804, which compares the pressure values to target valuesthroughout the injection cycle. The controller then displaces the valvepins, according to whether an increase or a decrease in materialpressure is called for by the target profiles. According to onepreferred embodiment, the target profiles are executed by, for example,a PID algorithm stored in the controller 804.

The controller 804 can include a programmable logic controller (PLC) toprovide input/output connections. For example, the PLC can be used tocapture the material pressure data from the pressure transducers 69(a)and 69(b), and also provide control signals to servo valves 802. Thecontroller 804 is connected to both the servo valves 802 and thehydraulic power source 808 to monitor and control the hydraulic powersource. The operator interface 805 is, for example, the same asinterface 214 described with reference to FIGS. 14-18 above.

A complete control system 800 is shown in FIG. 32 which includes aninjection molding machine 806, which injects material into manifold 15via nozzle 11. The machine includes a reciprocating screw 809 which isused to force material out of the injection molding machine fed fromhopper 816. The screw is attached to a hydraulic actuator 818 which iscontrolled by the machine controller 812 which includes an operatorinterface 814. Pressurized hydraulic fluid is supplied to the actuatorvia an injection molding machine hydraulic power unit 810. Using theoperator interface, a user can set injection time, injection pressure,pack pressure, pack time, etc., for any given injection cycle.

In addition to controlling the rate of material flow through eachcontrol zone, the controller 804 also interfaces with the injectionmolding machine in several ways. The controller 804 is coupled to theinjection molding machine controller 812. The injection molding machinecontroller 812 can provide several different signals to the controller804. For example, the controller 812 can indicate to the controller 804that all gates and guards on the injection molding machine are closedand the machine 806 is in a state in which injection can occur. Thissignal should be received while the controller 804 is performing itscontrolling functions during the injection cycle.

The injection molding machine also can include an emergency stop buttonwhich could be wired to the controller 804 in which the controller 804would not perform controlling operations if the emergency stop isindicated. The controller 812 also can provide a signal to thecontroller 804 to indicate the start of injection based on physicalcharacteristics of the injection molding machine. This signal is toremain high until the end of injection and pack. Accordingly, thecontroller 804 can use this “start of injection” signal to begin controlaccording to the target profiles. For example, the rising edge of thestart of injection signal can indicate to the controller 804 that thestart of injection has begun.

A start of injection signal can also be provided to controller 804 by alinear position transducer 820 indicating that the screw 809 is in aposition in which injection has begun. Another way to provide a start ofinjection signal is to measure the pressure of the material in themachine nozzle 11 by a pressure transducer 820 coupled to controller804. Basing the start of injection signal on these physical readingsassociated with the injection molding machine can insure that adequatepressure is being supplied to the manifold when the controller 804begins executing the target profiles.

It is also desirable to provide an end of injection signal to thecontroller 804. One way to provide such a signal is to detect thefalling edge of the injection molding machine “on” signal describedabove. The end of injection signal can also be indicated by the risingedge of an “injection molding machine injection complete” signalprovided by controller 812. Lastly, the controller 804 itself canprovide an end of injection signal, when all profiles have beencompleted. Thus, the end of injection signal is used to indicate toeither the injection molding machine 806, the controller 804 or both,that the injection process is completed and all injection functionalityshould be discontinued.

The injection molding machine 812 can also provide a signal to thecontroller 804 that the injection molding machine has transitioned from“injection pressure” to “pack pressure.” According to one embodiment,controller 804 can use this signal to determine when the injectionmolding machine is transitioning and determine if said transitioning isprior to the target profiles transitioning to a pack pressure. Thisearly transitioning of the injection molding machine can result in acavity or cavities not filling entirely. Thus, controller 804 could usethis signal to generate a warning message via operator interface 805 ifearly transitioning occurs.

The injection molding machine controller 812 can also provide a signalto the controller 804 that the injection molding machine has reached theend of its injection forward sequence (i.e., that the screw 809 hasreached its forward-most position). The controller 804 could use thissignal to alert an operator via operator interface 805 if the injectionmolding machine has stopped injecting before all of the target profileshave been completed. This signal can also be used to indicate that cycletimes are not being minimized if the injection molding machine is stillinjecting after the controller 804 has completed all target profilesduring the injection cycle.

The injection molding machine controller 812 may also provide a signalas to when the pre-decompression (when the screw 809 is reset prior toplastication), or decompression (when the screw 809 is reset afterplastication), is complete. The signal can be used to indicate when thecontroller 804 can close valve pins 41(a) and 41(b) (i.e., withdraw thevalve pins 41(a) and 41(b) until the manifold channels are closed) to bein position for the next injection cycle. If this signal is notprovided, the controller will simply set a period of time from the endof the injection cycle to close the valve pins 41(a) and 41(b).

The controller 804 also can communicate signals to the injection moldingmachine controller 812. The controller output interface 805 can alsoinclude an emergency stop as described above with respect to theinjection molding machine. This emergency stop signal can be sent to thecontroller 812 and will act to halt the injection molding machine. Thecontroller 804 can also provide a signal indicating to the controller812 that the controller 804 is resident and must be interfaced with. Thesignal can be carried, for example, by a jumper cable connecting bothcontrollers. The jumper will complete an input circuit with theinjection molding machine indicating that the controller 804 isresident.

The controller 804 can also provide a “ready” signal to controller 812indicating that the hydraulic power source 808 is ready and that noalarms are present that would inhibit injection.

Controller 804 can also provide a signal to controller 812 indicatingthat all target profiles being executed by controller 804 havetransitioned from the fill stage of injection to the pack and holdstage. In one embodiment, the injection molding machine uses the signalto unload the high volume pumps no longer necessary in the pack and holdstages. Another use of the signal is to trigger the start of gasinjection for a gas assist application. The target profile of theinjection cycle would end after injection of melt material after whichgas is used to pack up the part.

The controller 804 can also provide a signal indicating that all thetarget profiles have been completed. The signal can then be used toabort the injection molding machine cycle and thus reduce wasted cycletime. This signal can also be used to indicate that cycle times are notbeing minimized if the injection molding machine is still injectingafter the target profiles are completed. Accordingly, this informationcould be used to reset the injection molding machine cycle time.Controller 804 can also provide a signal to the injection moldingmachine indicating that there was a control problem during the injectioncycle and therefore a high likelihood that the parts could be faulty.

The system 800 also includes cavity pressure transducers 824 and 826.These transducers provide useful information related to the moldingprocess. The transducers can be used to monitor and display cavitypressure via pressure profile curves for each control zone. Thisinformation can be used for trouble shooting to determine if any processchanges have occurred. The information can also be used for statisticalprocess control to ensure that the process stays within determinedoperating limits. For example, pressure readings from these pressuretransducers can establish acceptance criteria for peak pressure, packpressure, average pressure, area under the pressure curve, or otherpressure values during the injection cycle. Parts created during a cyclein which these criteria were not met can be rejected, or at least anotification can be generated at the operator interface 805 to warn theoperator.

The use of cavity transducers 824 or 826 provides greater control of theprocess. For example, if one of the transducers consistently registerstoo high or too low a pressure at a particular point in the injectioncycle, the target profile associated with that control zone can bealtered accordingly, using operator interface 805. This can beespecially useful in a large part having multiple gates. Placing cavitytransducers at multiple points along the cavity provides information onhow the part fills during the process and, if the part is not fillingproperly, on which target profiles of which control zones should bealtered and how they should be altered.

Transducers 824 and 826 can also be used to trigger switchover in thetarget profiles (and/or the injection molding machine) from injectionpressure to pack pressure. In the embodiments described above switchoverfrom injection pressure to pack pressure is determined by the targetprofiles according to time, however, using the pressure transducers, aset point pressure can be established at which time the target profileswitches to the “pack” area of the profile, independent of time. Thiscan be done for each target profile separately, as there would be acavity pressure transducer associated with each control zone. Thisvariable can also be used to control when the injection molding machineswitches from injection pressure to pack pressure.

Switchover can also be controlled by placing transducers at either endof cavity 5. When the pressure transducers detect material pressure atthe end of the cavity, the controller 804 can switch the control zone(or zones) associated with that end of the cavity to the “pack” portionof the target profile. This method of controlling “switchover” canaccount for variations in material viscosity which can cause the part tofill more quickly or slowly, thus, making a time-based “switchover”inexact.

Controlling “switchover” is also useful in multiple cavity applications,as shown in FIG. 35. In a mold have multiple like cavities 5 a and 5 b,ideally the controller 804 would “switchover” each control zone (one foreach cavity when each cavity has a single gate) from injection to packat the same point in time during the injection cycle. Material and flowvariations in the multiple cavities, however, may cause the fillingrates to be slightly different from one cavity to the next. Using apressure transducer in each cavity 5 a and 5 b to trigger switchoverindependently for each control zone, as described above, compensates forthese variations and can improve the repeatability of the process.Alternatively, the cavity pressure transducer can be used to “tweak”each target profile to create uniform cavity pressure readings (anduniform parts) from each cavity. In the multi-cavity application thepressure transducer can be located adjacent the gate similarly to FIG.32, or at an end of each cavity 5 a and 5 b as shown. As describedabove, either location can be used to control switchover.

The cavity pressure transducers can also be used to determine the end ofthe pack period, unlike previous embodiments in which the profile itselfdictates the end of pack at a particular time after the start ofinjection. Again referring to FIG. 35, transducers located at the end ofthe cavities 5 a and 5 b, can be used to determine the end of the packperiod for individual cavities (or a single cavity) by indicating whenthe pressure at the end of the cavity reaches a particular value duringpack indicating that the part is filled. Thus, the end of pack can beindependently set in each control zone according to when a particularpressure is detected. If an extended valve pin is used (see FIGS.11-15), the valve pins can be closed according to this pressure-basedend of pack determination. The use of pressure to determine end of packensures consistent part weight by compensating for flow variationswithin the cavity or cavities which may change from shot to shot.

For cascade molding, cavity pressure transducers can be used to indicatethe arrival of the material flow front at a gate downstream of theinitial gate opened. Once the flow front is past the downstream gate,the cavity pressure transducer will see a rise in pressure. Thecontroller 804 can then start the injection at the next gate based on adetermined pressure set point measured by the cavity pressuretransducer.

As shown in FIG. 32, the controller 804 also interfaces with machinenozzle pressure transducer 822. As explained above, this pressure can beused by the controller 804 to start the target profiles, and also beused to ensure that the supply pressure is high enough to run theprocess. If the injection molding machine 806 is supplying an inadequatepressure, a signal could be generated by the controller 804 anddisplayed on the operator interface 805.

The controller also interfaces with a linear transducer 820 thatmeasures the position of the ram 809 and can be used as an indicator ofthe volume of material injected into the part. “Switchover” frominjection pressure to pack pressure in both the target profiles and theinjection molding machine (described above) can also be based on a setpoint value associated with linear transducer 820 indicating that theproper volume of material has been injected into the mold.

FIG. 33 shows an alternative embodiment similar to the system shown inFIG. 32. In this embodiment, however, the hydraulic power source 808 hasbeen eliminated and servo valves 802 are connected directly to theinjection molding machine hydraulic power unit 810. Thus, hydraulicpower to servo valves 802 used to manage the flow of pressurized fluidto actuators 49(a) and 49(b) comes directly off the injection moldingmachine power unit 810, and this configuration saves the expense ofhaving a separate power source 808 to supply servo valves 802. Thesystem is the same as the system shown in FIG. 32 in all other respects.

Several other alternative configurations are possible with respect toFIG. 33. For example, an accumulator (not shown) can also be connectedto the hydraulic power unit 810 to ensure a steady supply of pressurizedfluid to servo valves 802 of which there is a single servo valve foreach actuator 49(a) and 49(b). Also, the servo valve 802 may be mountedto the injection molding machine directly or to the mold as shown.

FIG. 34 shows another alternative embodiment of a injection moldingsystem similar to the system shown in FIG. 33. In FIG. 34, however, thecontroller 804 and operator interface 805 has been integrated as part ofthe injection molding machine controller 830 and 832. Controller 830 andoperator interface 832 perform the functions of controllers 804, 812,and operator interfaces 805 and 814 of FIGS. 32 and 33. This integrationsimplifies the system and reduces the hardware in the system.

The integration can be performed by simply mounting the programmablecontroller described above within controller 804 into the injectionmolding machine control cabinet which contains controller 812. In such acase the input and output functions performed by controller 804 wouldstill be performed by the same PLC. Alternatively, a single PLC or othertype of controller can be used to interface all injection moldingmachine controller functions and functions performed by controller 804.The operator interface 832 performs the functions of both operatorinterfaces 805 and 814 of FIGS. 32 and 33 and interfaces directly withthe PLC that controls servo valves 802 for menus, set-up displays ofprocess readings, and other functions.

The hydraulics in FIG. 34 are the same as in FIG. 33 with servo valves802 being supplied hydraulic power by injection molding machinehydraulic power unit 810. Alternatively, separate hydraulic powersources can be used as shown in FIG. 32.

FIG. 36 shows a flow chart representing a method of open-mold purgingaccording to another embodiment of the invention. To effect a materialchange when molding (e.g., a change in material color, grade, type,etc.), it is usually necessary to purge the injection molding system,including the manifold and the injection nozzles, of the materialcurrently be used. Two methods of purging are generally known. Onemethod is to simple change materials and mold parts until the previousmaterial is completely purged. This method, however, can be timeconsuming and therefore costly, since it requires running repeatedinjection cycles.

The second method is called “open-mold” purging. As the name indicates,in open-mold purging, the mold is opened, and the injection moldingmachine screw is run “manually” as a non-reciprocating extruder whilethe injected material is flushed through the manifold and nozzles andinto the area separating the open mold halves. This method of purgingthe injection molding system is faster, and therefore less costly, thanrunning repeated injection cycles.

In a typical valve-gated injection molding application, the valve pin issimply moved into the retracted “open” position (as it is during aninjection cycle), the mold is opened, and the injection molding machinescrew is turned on. In a thermal-gate application having no valve pin,purging is accomplished simply by opening the mold and turning on theinjection molding machine screw.

In the flow-control applications described herein, purging can be morecomplicated due to the geometry of the various valve pins. Theembodiment shown in FIGS. 1-5, utilizes a “reverse-taper” valve pin 41to control the flow, but is a thermal-gate application because the pindoes not close the gate. During open mold purging, the valve pin of thisembodiment should be in a fully-forward position to permit the maximumflow of purge material through the system, so that purging can beaccomplished as quickly and efficiently as possible.

Thus, to purge in a system that uses the type of valve pin shown inFIGS. 1-5, the servo valves that energize the actuator 49 to control themotion of the of the valve pin can be set in a fixed position thatbiases the pin fully forward. This can be accomplished by manuallysetting the servo valves, or by programming a pressure profile into thecontroller (PID1, PID2, CPU) having a high constant target pressure tocause the valve pin 41 to move into the fully forward position. Forexample, if the target pressure is set at 10,000 p.s.i., and the highestpressure that the injection molding machine can supply to the pressuretransducers 69 (PS1 and PS2) is 7,500 p.s.i., the controller will signalthe servo valves to cause the actuator 49 to move the valve pin fullyforward, calling for an increase in pressure as dictated by the purgepressure profile.

In the case of the valve pin shown in FIGS. 13-15, the valve pin 200 hasa reverse taper control surface 205, and has an extended section toclose the gate. The difficulty with this type of pin design, asdiscussed above, is that if the pin moves too far forward, the end ofthe pin will begin to close the gate inadvertently. Thus, if the methodof purging explained above with respect to the reverse taperthermal-gate valve pin of FIGS. 1-5 is used, the controller 210 willsignal the actuator to keep moving the valve pin forward in an attemptto achieve the 10,000 p.s.i. target pressure (which, as stated above, ishigher than the maximum pressure supplied at transducer 217), until thepin inadvertently closes the gate. To avoid this problem the method ofopen mold purging depicted in the flow chart of FIG. 36 has been createdto enable the system to achieve a maximum purge flow while preventingthe valve pin from closing the gate.

According to the foregoing preferred method of open mold purging, instep 900 the user selects a target purge pressure profile. This isperformed similarly to the manner in which a user selects a targetpressure profile during an injection cycle when molding parts, asexplained above with reference to FIGS. 17 and 18 (edit and selectprofile figures). The purge profile, however, is typically a rectangularprofile having a constant pressure setpoint, as shown in FIG. 37 (targetpurge pressure of 3,000 p.s.i.). The target pressure value is selectedso that the valve pin is as close to a “fully forward” position aspossible, without the end 227 of the valve pin being in a position tohinder or close flow through the gate.

Thus, in step 900, the pressure should be selected to be significantlylower than the machine delivery pressure to prevent continued forwardmovement from the valve pin, yet high enough so that the control gap 207between the pin and the manifold does not substantially restrict theflow of purge material. Of course, the ideal target value of pressurewill be different from machine to machine, application to application,and material to material, thus, different target values may have totested to determine what value will work for a particular application.By way of example, a target purge pressure of 3,000 p.s.i. has beenshown to work for a machine delivering 15,000 p.s.i. to a manifoldhaving four injection nozzles coupled thereto. FIG. 37 depicts a screenicon displayed on interface 214 that shows the actual pressure 905sensed by the transducers 217 tracking the target purge pressure 915,which is a rectangular constant pressure profile.

The target purge pressure is entered via a graphical user interface iconsimilar to those shown in FIGS. 17 and 18, which preferably enables theuser to select a “purge” mode, and which then prompts the user to selecta purge pressure. After selecting a desired target purge pressure, themold is opened in step 910. In step 920, purging begins by starting theinjection molding machine in manual non-reciprocating extruder mode.

Preferably, the injection molding machine provides the controller 210with a start of injection signal, with which, upon receipt, thecontroller begins to control the valve pin to yield the target purgepressure. Some machines, however, do not provide such a signal when themold is opened and the machine is run in manual mode as an extruder.Thus, in such a case the user can manually start both the injectionmolding machine and instruct the controller to begin purge mode.

Unlike a normal injection cycle in which a part is being molded, thetiming between the machine and the controller is not critical, as thepurge time is not preset and is determined by the machine operator. Forexample, flow-control by the controller 210 can begin before the machinestarts injection. In such a case, the pin will travel fully forward andclose the gate in attempting to attain the target purge pressure. Onethe machine begins injection, the pressure detected by the transducer217 will quickly become higher than the target purge pressure becausethe gate is closed, and controller will cause the pin to retract toreduce the pressure and track the target purge pressure. The profile inFIG. 37 shows this method, as the profile indicates that the controllerbegan reading pressure values before the machine has been turned on,resulting in a several millisecond period that the actual pressure 905is zero prior to the machine is turned on. Thus, purging is accomplisheddespite the fact that the timing between the injection molding machineand the controller is not exact.

Another way to time the start of injection and the start of flow controlaccording to the purge target profile, is to move the valve pins forwardto close the gate when the operator selects purge mode. Typically, whenthe controller begins to control according to a target profile, the pinsare fully retracted, and move forward when the profile calls for anincrease in pressure. By moving the pins forward prior to injection, thestart of flow control can be triggered when the pressure transducersdetect a particular pressure, e.g., 200 p.s.i. When the pressure isdetected the controller will begin flow control according to the purgeprofile, and will cause the valve pin to be retracted to lower thepressure, since the pressure will quickly rise above the purge pressurewith the gates closed. Thus, using this alternate method of beginningpurging, flow control will begin at substantially the same time asmachine injection, but requires the additional functionality of thecontroller moving the pins to close the gate when the operator selectsthe purge routine.

In step 930 the operator stops the purge routine by turning off themachine and ending the purge control profile. The operator makes thisdetermination based on experience and inspection of the material.Accordingly, when the controller 210 is executing the purge profile, a“stop purge” button is displayed on the graphical user interface so thatthe operator can end the purge routine being executed by the controllerby pressing a single button. The controller will instruct the actuatorto retract the pins to the starting position when the operator stops thepurge routine. At this time the injection molding machine can bereturned to automatic mode, a target profile can be programmed into thecontroller, and parts can be molded using the new material.

It should be understood that usually the purge routine will be carriedout for all injection nozzles coupled to the manifold, and that thepurge pressures are the same for each nozzle. However, as describedherein, the pressure profiles for each nozzle are independentlyprofitable, thus, different purge pressures can be chosen for differentnozzles, and all nozzles need not be purged at the same time, i.e., thegate to one or more nozzles can remain closed while the remainingnozzles are purged.

Having thus described certain embodiments of the present invention,various alterations, modifications, and improvements will readily occurto those skilled in the art. Such alterations, modifications, andimprovements are intended to be within the spirit and scope of theinvention. For example, in the embodiments shown in FIGS. 31-33,although only two gates are shown to a single cavity 5, more gates (andassociated nozzles, valve pins, actuators and servo valves, i.e.,control zones) may be used which gate into one or more cavities.

Additionally, servo valves 802 are shown in FIGS. 32-35 (and previousembodiments), however, the invention is not so limited and other typesof valves such as proportional valves may be used. Also, althoughhydraulic actuators 49 a and 49 b are used in FIGS. 32-35 (and previousembodiments), pneumatic or electronic actuators can be used to controlthe valve pins (for example, the electronic actuators disclosed inco-pending patent application Ser. No. 09/187,974 entitled ELECTRONICACTUATOR FOR PIN). Thus, the invention is not limited to a particulartype of actuator. Further still, although a hydraulic-powered injectionmolding machine is shown in FIGS. 32-35, the invention is not limited toa particular type of injection molding machine. For example, anelectronic injection molding machine could be used.

Accordingly, the foregoing description is by way of example only, andnot intended to be limiting. The invention is limited only as defined inthe following claims and the equivalents thereof.

What is claimed is:
 1. A method of open-mold purging in an injectionmolding system including a manifold to receive material injected from aninjection molding machine, comprising the steps of: (A) selecting atarget purge pressure; (B) injecting material from the injection moldingmachine into the manifold; and (C) controlling the purge pressure tosubstantially track the target purge pressure; wherein the purgepressure is controllable between the injection molding machine and thegate independently from the injection molding machine pressure.
 2. Themethod of claim 1, wherein step (A) includes selecting a target purgepressure that is greater than the pressure supplied by the injectionmolding machine.
 3. The method of claim 1, wherein step (A) includesselecting a target purge pressure that is less than the pressuresupplied by the injection molding machine.
 4. The method of claim 1,wherein step (C) is performed inside the manifold.
 5. The method ofclaim 1, wherein step (C) is performed inside an injection nozzle.
 6. Aninjection molding system comprising: a mold; an injection moldingmachine; a manifold; and a controller used to control open mold purgingof the manifold, wherein the controller controls a pressure of materialused to purge the manifold, independently from the injection moldingmachine injection pressure and between the injection molding machine andthe gate.
 7. The injection molding system of claim 6, wherein thecontroller controls the pressure of material based on a selected targetpurge pressure.
 8. An injection molding system comprising: a manifold todeliver material into a mold that is injected into the manifold from aninjection molding machine; and a controller used to control open moldpurging of the manifold, the controller to control a pressure ofmaterial used to purge the manifold, independently from the injectionmolding machine injection pressure and between the injection moldingmachine and the gate.
 9. The injection molding system of claim 8,wherein the controller controls the purge pressure using a valve pin.10. The injection molding system of claim 8, wherein the controllercontrols the purge pressure inside the manifold.